leak between radiator and transmission shouldnt be too difficult to solve dont know your car specifically but automatic transmissions tend to have a line that runs fluid through the radiator to cool it its possible you could solve that leak fill the tranny fluid and park strategically to avoid having to reverse but yeah if you havent done much car work yourself you need a friend that knows what theyre doing probably also need a friend with tools even then theres no guarantee the junkyard transmission is in good shape on the flip sideevery other car under k is going to be a similar gamble especially if you dont know what issues to look for i will say you should be able to get at least a few hundred more selling your car on craigslist